Automatic intercept two-channel radio receiver



Feb. 15, 1938. c T s 2,108,088

AUTOMATIC INTERCEPT TWO-CHANNEL RADIO RECEIVER Fined July 17, 1954 s Shets-Sheet 1 flMLQL CIF pm Q3 007F07- A 5 I Y IN V EN T 0R.

C. R. TUFTS Feb. 15', 1938.

AUTOMATIC INTERCEPT TWO-CHANNELRADI O RECEIVER I I s Sheets-Sheet 2' mw n Filed July 17, 19 4 HSQWERNx ATI "ORNEY Feb. 15, 1938. c. R. TUFTS AUTOMATIC INTERCEPT TWO-CHANNEL RADIO RECEIVER Filed July 17, 1954 3 Sheets-Sheet 5 INVENTOR. J

i ATTORNEY Patented Feb. 15, 1938 UNITED STATES AUTOMATIC INTERCEPT TWO-CHANNEL RADIO RECEIVER Carl R. Tufts, Detroit,

Mich, assignor of onethird to Edwin L. Powell, Washington, D. C., and one-third to Charles E. Motto, Detroit,

Mich.

Application July 17, 1934, Serial No. 735,694

12 Claims.

My invention relates broadly to multi-channel high frequency signaling systems, and more particularly to an automatic arrangement for the selective operation of any one channel of a signaling 5 system.

One of the objects of my invention is to provide a signal receiving system which includes a plurality of tuned circuits each resonant to a different signal frequency and automatic means for interrupting the normal operation of one circuit when signal energy is incident onv another circuit.

Another object of my invention is to provide an automatic multi-channel selective high frequency signal receiver of the superheterodyne type employing the same intermediate frequency amplifiers, second detector and audio frequency amplifiers for operation of the receiver on any of the signal channels. Still another object of my invention is to provide an electron tube control circuit, operative upon the incidence of signal energy upon one channel of a multi-channel high frequency signal receiver, to automatically increase the bias on the control grids in the electron tubes in the circuits constituting the normally operative channel to the cut-off point.

A further object of my invention is to provide a high frequency signal receiver normally operative for the reception of signal energy at a frequency within a certain frequency band but automatically and instantaneously responsive to sig nal energy at a predetermined frequency within another frequency band incident upon an auxiliary tuned circuit, to the exclusion of the signal energy normally received.

A still further object of my invention is to provide an arrangement of automatic control circuit whereby the bias potentials on the control grids of electron tubes in a tuned circuit normally employed, are increased to the cut-off point when signal energy is received in a second tuned circuit.

Another object of my invention is to provide a multi-channel automatically selective high frequency signal receiver employing an automatic control circuit energized by signal energy received through one channel and effective on another channel, and acting to interrupt normal reception through the last mentioned channel so long as signal energy is received through the first mentioned channel.

Still another object of my invention is to provide an automatically selective multi-channel superheterodyne receiver employing the same intermediate frequency amplifier, and means for preventing interference between the frequencies of the conversion oscillators and. possible interference therefrom.

Other and further objects of my invention reside in the circuits and arrangements more fully described in the following specification with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of the arrangement of myinvention applied to a superheterodyne high frequency signal receiving system; Fig. 2 is a block diagram of the arrangement when pre-selector or tuned radio-frequency amplifier stages are used before the converter circuits; and Fig. 3 is a wiring diagram showing a modified arrangement of control'units in a multiple intercept receiver embodying the system of my invention.

My invention fulfills the need for a radio receiver which normally responds to any given signal in one frequency band, and which will automatically shift to respond to another desired frequency for the duration of this last mentioned frequency; for example, a receiver which normally can be tuned to receive on any of the channels employed for marine communication, and which will automatically shift to 500 kilocycles at any time that a distress signal is transmitted. The circuit hereinafter described and shown in Fig. 1 is a receiving system which normally responds to any desired frequency in the broadcast band but which automatically shifts to the emergency service band at the instance of any transmission from a previously selected police or emergency signal transmitter operating in that band.

Thus, antenna I, transformers 3, 4, 5o, 6, l, and

8, and electron tubes l5, IE, IT, !8, and [9 constitute a superheterodyne receiver for broadcast reception. This is similar to well-known circuits except for the control grid biasing circuits of tube 15, which will be described later. A frequency of 175 kilocycles may be employed for the intermediate frequency, the difference frequencybeing used in conversion, that is, the difference between the frequency of the signal received and the intermediate frequency is the frequency of the conversion oscillator. Hence, transformer 3 responds to the band 550 to 1570 kilocycles and transformer 4 covers the range of 375 to 1395 kilocycles. Automatic volume control is obtained in the diode portion of tube is, which functions as the second detector, the biasing voltage developed in the load resistor 23 controlling the potential on the grids of the two intermediate frequency amplifier tubes I6 and ll. The desired output level is obtained by adjustment of the potentiometer 24 which controls the audio frequency voltage fed to the control grid in the triode section of the tube l8, which functions as the first audio frequency amplifier stage.

Similarly, antenna 2, transformers 9, ll], 5b, 5, i, and 8, and electron tubes 20, l6, [1, I8, and i9, constitute a superheterodyne receiver for police reception. This is similar to well known circuits except for auxiliary means inserted in the screen-grid circuit of tube which will be described later. The frequency of 175 kilocycles is employed for the intermediate frequency amplifier, these circuits being common to those for the broadcast receiver, but the sum frequency is used in conversion, that is, the sum of the frequency of the signal received and the intermediate frequency is the frequency of the conversion oscillator. Hence, transformer 9 responds to the band 1658 to 2490 kilocycles and transformer It! covers the range 1833 to 2665 kilocycles. Thus, by making the conversions in the two-receiver combination by using the sum and the difference frequencies as related, there is no interference between the two conversion oscillators, nor will they combine to produce a beat frequency which would be amplified in the intermediate frequency amplifier stages.

The primary of transformer [2 which is also tuned to 175 kilocycles, is tapped into the screengrid circuit of the pentagrid converter tube 20, and its secondary excites the control grid of the triode section of the duo-diode-triode tube 2|, giving a stage of 1'75 kilocyc'le amplification electronically coupled from the converted output of the first detector of the police or emergency band receiver system. The output of the triode section of the tube 2| is fed through transformer i l, also tuned to 175 kilocycles, to the diode section of the tube 2|. Thus, this amplified 1'75 kilocycle current, when present, is detected in the diode circuit of tube 2| through a load resistor 25, the IR drop across which furnishes an additional negative voltage in series with the normal negative voltage furnished by the cathode resistor 26 of tube l5 for automatically cutting off the operation of the broadcast band system.

In operation, the input circuits of the police band system are tuned to the frequency of the desired police transmitter, and left fixed. The input circuits of the broadcast band system may be tuned at will to any frequency in the broadcast spectrum. So long as no incoming wave is converted in the first detector circuit of the police band system, no additional voltage is developed in resistance 25, hence the control grid of tube l5 operates at the normal bias voltage developed in the cathode resistor 26, and the equipment functions as a broadcast receiver. When the police wave excites tube 20, however, the equipment immediately responds to that signal because the additional negative voltage developed across resistance biases tube l5 to cut-off. The foregoing is true only when switch 2'! and switch 28 are closed. With switch 21 open and switch 28 closed, the equipment operates only as a normal broadcast receiver. With switch 2? closed and switch 28 open, the equipment functions only as a normal police receiver. In practice, these two switches may be ganged together for operation by a single three-position control knob.

The two circuits are shown in Fig. 1 without any pre-selector radio frequency amplifier stages for the sake of simplicity in illustrating the action of the invention. In practice, however, a circuit employing a super-control tube such as the type 6D6, would be introduced at the input of each receiver system for reduction of image response. The tube for the police band system may operate at a fixed normal bias furnished by its associated cathode resistor; but the control grid of the one for the broadcast band system should be connected back to the automatic cutoff biasing circuit, in parallel with that of the pentagrid converter in the broadcast band system. Such an arrangement is shown in outline in Fig. 2.

A plurality of intermittently used systems may be employed as shown in Fig. 3, each responsive to a diiferent frequency of transmission. The control units in each case are energized as before and all are effective on the control grids of the tubes in the normally used system. When any one of the intermittently used systems is energized, therefore, the signal energy passed therethrough will be heard to the exclusion of the normally received energy.

Fig. 3 is a schematic diagram similar to the showing in Fig. 1 wherein the elements of the second intermittently used system are indicated by primed reference characters corresponding to those applied to like elements of the intermittently used system shown in Fig. 1. The output of the additional circuit, taken from the anode of the pentagrid converter tube 20, is coupled through the transformer section 50 to the intermediate frequency amplifier tube It in a manner similar tothe coupling of the output of tube 20 through the transformer section 51). The

output of the amplifier tube I6 is coupled through transformer 6 with the remainder of the receiving circuit shown in Fig. l. Cut-01f bias potential produced in resistance 25 is applied to the control grid of tube l5 similarly to the arrangement for resistance 25, and likewise in the negative sign.

It will be understood that transformers 9' and ID are tuned to select a signal of a frequency quency range similar to that of transformer 9, and Ill, and that the intermediate frequency produced in the same, 175 kilocycles in the example stated. Transformer 9' may respond to a frequency range similar to that of transformer 9, or a higher range, and conversion with the local oscillation is effected in the same manner as in the first auxiliary selector circuit; that is, transformer I0 is tuned to a range of frequencies respectively 175 kilocycles greater than the corresponding frequencies in the range of the transformer 9.

But one condition must be observed, which is that the frequencies of the local oscillators in the auxiliary selector circuits, as determined by the set tuning of transformers l0 and Ill, shall not be of such values as to beat at a frequency within the range of the intermediate frequency amplifiers, for such would result in interference With the normally received signal at the intermediate frequency. This indirect interference condition is only a remote possibility in the operation of the system, and for all practical purposes may be readily overcome, either by adjusting one of the auxiliary selector circuits to a different frequency, or opening the switch 27 or 21' of the circuit tuned to the less desired signal.

In Fig. 3 the power supply circuits are merely indicated, the heater connections marked H, H, being intended for connection to the source H, H, shown in Fig. 1, and the automatic volume control bias potential in the line A. V. C., the anode potential, and the screen grid potential, being derived in the manner clearly shown in Fig. 1.

I may employ the system of my invention in a receiving system having tuned radio frequency channels in lieu of superheterodyne receiving circuits, in which case, a common detector and amplifier may be used for each of the channels.

While I have described my invention in certain of its preferred embodiments, I desire it to be understood that modifications may be made and that no limitations upon my invention are intended other than may be imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In a multi-channel high frequency signal receiving system, a normally operative selector circuit, a plurality of auxiliary selector circuits, said normally operative selector circuit including an electron tube having anode, cathode, and control electrodes, said auxiliary selector circuits in eluding electron tubes having anode, cathode, control, and screen electrodes, automatic control means individual to each of said auxiliary selector circuits, and electronically coupled thereto through said screen electrodes and connected in common to the control electrode in the electron tube in said normally operative selector circuit, said automatic control means being individually operative by signal energy received through the respective auxiliary selector circuit to produce cut-off bias potential on said control electrode to render inoperative said normally operative selector circuit for the duration of said signal en- 2. In a multi-channel superheterodyne high frequency signal receiving system, a plurality of signal receiving channels, means for normally receiving signal energy through one channel, means for automatically effecting inoperation of said channel for receiving different signal energy through another channel for the duration of said last mentioned signal energy, each of said channels including the selective conversion elements for an independently controlled superheterodyne receiving circuit.

3. In an apparatus of the class described a pair of signal receiving channels, means for selectively tuning each of said channels over different frequency ranges, frequency converting means having an oscillator portion and an amplifier portion individual to each of said channels, an intermediate frequency amplifier connected with said frequency converting means, signal observing means coupled to said intermediate frequency amplifier, means for tuning each of said frequency converting means over frequency ran es for insuring the generation of oscillator requencies which will not combine to produce the intermediate frequency while producing with respect to signalling energy incident upon the respective channels the same intermediate frequency, and means for interrupting the transfer of signalling energy through one of said channels responsive to signalling energy incident upon the other of said channels.

4. An automatic intercept multi-channel signal receiving system comprising in combination a pair of signal receiving circuits, frequency converting means individual to each of said circuits, an intermediate frequency amplifier connected to each of said frequency converting means, signal observing means connected with said intermediate frequency amplifier, means selectively tuning one of said circuits over a predetermined frequency range, means for selectively tuning the other of said signal receiving circuits over a different frequency range, means individual to each of said frequency converting means for tuning said frequency converting means over frequency ranges for producing the same readily amplifiable intermediate frequency with respect to the signal energy incident upon the respective signal receiving circuits, and means for interrupting the transfer of signalling energy from one of said signal receiving circuits responsive to a signal incident upon the signal receiving circuit connected with the other of said frequency converting means.

5. In an apparatus of the class described, a pair of signal receiving channels, means for selectively tuning each of said channels over different frequency ranges, frequency converting means having an oscillator portion and an amplifier portion individual to each of said channels, an intermediate frequency amplifier connected with said frequency converting means, signal observing means coupled to said intermediate frequency amplifier, means for tuning said frequency converting means over frequency ranges for insuring the generation of oscillator frequencies which are so widely separated in the frequency spectrum that the oscillator frequencies do not combine to produce the intermediate frequency while producing with respect to the signalling energy incident upon the respective channels the same intermediate frequency and means for interrupting the transfer of signalling energy through one of said channels responsive to signalling energy incident upon the other of said channels.

6. In an apparatus of the class described, a pair of signal receiving channels, means for selectively tuning each of said channels over different frequency ranges, frequency converting means having an oscillator portion and an amplifier portion individual to each of said channels, an intermediate frequency amplifier connected with said frequency converting means, signal observing means coupled to said intermediate frequency amplifier, I

a tuned input circuit for said intermediate frequency amplifier, a tuned output circuit connected with the amplifier portion of each of said frequency converting means, all of said tuned circuits being mutually coupled for the transfer of energy through said intermediate frequency amplifier, means for interrupting the transfer of signalling energy through one of said channels responsive to signalling energy incident upon the other of said channels.

7. In an apparatus of the class described, a pair of signal receiving channels, means for selectively tuning each of said channels over different frequency ranges, frequency converting means having an oscillator portion and an amplifier portion individual to each of said channels, an intermediate frequency amplifier connected with said frequency converting means, signal observing means coupled to said intermediate frequency amplifier, the frequency of one of the oscillator portions of one of said frequency converting means being related to a selected sign-a1 frequency incident upon the signal receiving channel associated therewith for producing the intermediate frequency by a process of addition while the frequency of the oscillator portion of the other of said frequency converting means is so related to any selected frequency within the frequency range of the signal receiving channel associated therewith to produce the same intermediate frequency by a process of subtraction of the frequency of the oscillator portion of the last mentioned frequency converting means from the selected signal frequency, and means for interrupting the transfer of signalling energy through one of said channels responsive to signalling energy incident upon the other of said channels.

8. In an apparatus of the class described, a pair of signal receiving channels, means for selectively tuning each of said channels over different frequency ranges, frequency converting means having an oscillator portion and an amplifier portion individual to each of said channels, an intermediate frequency amplifier connected with said frequency converting means, signal observing means coupled to said intermediate frequency amplifier, the frequency ranges of the oscillator portions of said frequency converting means being so widely spaced as not to produce by mutual interaction a beat frequency Within the frequency range of said intermediate frequency amplifier, and means for interrupting the normal reception of signal energy through one of said signal receiving channels responsive to signalling energy incident upon the other of said signal receiving channels.

9. In an apparatus of the class described, a pair of signal receiving channels, means for selectively tuning each of said channels over different frequency ranges, frequency converting means having a tunable oscillator portion and an amplifier portion individual to each of said channels, an intermediate frequency amplifier connected with the respective amplifier portions of said frequency converting means, signal observing means coupled to the output of said intermediate frequency amplifier, each of said channels and its tunable oscillator portion being tunable in such manner that the sum or difference frequency between the received signal frequency and the frequency generated by the oscillator portion of its, frequency converting means produces the desired intermediate frequency, and means automatically interrupting the operation of the amplifier portion of one of said frequency converting means responsive to signalling energy incident upon the signal receiving channel individual to the other of said frequency converting means.

10. In an apparatus of the class described, a pair of signal receiving channels, means for selectively tuning each of said channels over different frequency ranges, frequency converting means having an oscillator portion and an amplifier portion individual to each of said channels, an intermediate frequency amplifier connected with said frequency converting means, signal observing means coupled to said intermediate frequency amplifier, means for tuning each of said frequency converting means over frequency ranges for insuring the generation of 0s.- cillator frequencies which will not combine to produce the intermediate frequency, while producing with respect to signalling energy incident upon the respective channels the same intermediate frequency, a circuit, a rectifier circuit, means coupling said rectifier circuit between one of the signal receiving channels and the amplifier portion of the other frequency converting means for interrupting the operation of the amplifier portion of said last mentioned frequency converting means responsive to signalling energy incident upon the other of said signal receiving channels.

11. In an apparatus of the class described, a pair of signal receiving channels, means for selectively tuning each of said channels over different frequency ranges, frequency converting means having an oscillator portion and an amplifier portion individual to each of said channels, an intermediate frequency amplifier connected with said frequency converting means, signal observing means coupled to said intermediate amplifier, means for tuning each of said frequency converting means over frequency ranges for insuring the generation of oscillator frequencies which Will not combine to produce the intermediate frequency while producing with respect to signalling energy incident upon the respective channels the same intermediate frequency, a control tube circuit electronically coupled with one of said signal receiving channels, and means controlled by said control tube circuit for interrupting the operation of the amplifier portion of the frequency converting means in the other of said signal receiving channels responsive to signalling energy incident upon the first mentioned signal receiving channel.

12. In a high frequency signal receiving system, a tun-able circuit, an electron tube device associated with said circuit, anode, cathode, and control electrodes included in said electron tube device, means for biasing the control electrode for operation of said electron tube; a tuned circuit, an electron tube device associated with said tuned circuit, anode, cathode, control, and screen electrodes in the last said electron tube device, a bias control circuit connected between said screen electrode and said means for biasing the control electrode in said first mentioned electron tube device, said bias control circuit including a rectifier device and a resistance device,

said bias control circuit being operative by high frequency signal energy passed by said tuned circuit to produce a voltage across the resistance device in said bias control circuit sufficient to impress cut-off bias potential on the control electrode of said first mentioned electron tube device; a single output circuit coupled With both said anode electrodes and adapted to be normally energized by signal energy selected in said tunable circuit, and by signal energy passed by said tuned circuit, to the exclusion of signal energy selected in said tunable circuit, When signal energy of the frequency of said tuned circuit is received.

CARL R. TUFTS. 

